We propose to study the aging lung of the nonhuman primate as a model of the aging lung of man. The mechanical properties of lung parenchyma (length-tension characteristics) and whole lung (pressure-volume (P-V) characteristics), the morphology and morphometry, will be examined. Changes in these measures with age, the correlation of structure and mechanical properties, and the comparative changes (man) will be investigated. Lung maturation will be defined by these techniques and distinguished from senescence. In addition, the naturally occurring and age-related destruction of the lung (emphysema) that is found in the nonhuman primate will exaggerate the changes in mechanical properties and structure of the lung to test our understanding of the relationship between structure and lung mechanics.